- Selective Construction of C?C and C=C Bonds by Manganese Catalyzed Coupling of Alcohols with Phosphorus Ylides
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Herein, we report the manganese catalyzed coupling of alcohols with phosphorus ylides. The selectivity in the coupling of primary alcohols with phosphorus ylides to form carbon-carbon single (C?C) and carbon-carbon double (C=C) bonds can be controlled by the ligands. In the conversion of more challenging secondary alcohols with phosphorus ylides the selectivity towards the formation of C?C vs. C=C bonds can be controlled by the reaction conditions, namely the amount of base. The scope and limitations of the coupling reactions were thoroughly evaluated by the conversion of 21 alcohols and 15 ylides. Notably, compared to existing methods, which are based on precious metal complexes as catalysts, the present catalytic system is based on earth abundant manganese catalysts. The reaction can also be performed in a sequential one-pot reaction generating the phosphorus ylide in situ followed manganese catalyzed C?C and C=C bond formation. Mechanistic studies suggest that the C?C bond was generated via a borrowing hydrogen pathway and the C=C bond formation followed an acceptorless dehydrogenative coupling pathway. (Figure presented.).
- Liu, Xin,Werner, Thomas
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p. 1096 - 1104
(2020/12/31)
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- Nickel-Catalyzed Esterification of Aliphatic Amides
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Recent studies have demonstrated that amides can be used in nickel-catalyzed reactions that lead to cleavage of the amide C?N bond, with formation of a C?C or C?heteroatom bond. However, the general scope of these methodologies has been restricted to amides where the carbonyl is directly attached to an arene or heteroarene. We now report the nickel-catalyzed esterification of amides derived from aliphatic carboxylic acids. The transformation requires only a slight excess of the alcohol nucleophile and is tolerant of heterocycles, substrates with epimerizable stereocenters, and sterically congested coupling partners. Moreover, a series of amide competition experiments establish selectivity principles that will aid future synthetic design. These studies overcome a critical limitation of current Ni-catalyzed amide couplings and are expected to further stimulate the use of amides as synthetic building blocks in C?N bond cleavage processes.
- Hie, Liana,Baker, Emma L.,Anthony, Sarah M.,Desrosiers, Jean-Nicolas,Senanayake, Chris,Garg, Neil K.
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p. 15129 - 15132
(2016/11/25)
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- Phosphorus oxychloride as an efficient coupling reagent for the synthesis of esters, amides and peptides under mild conditions
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A mild method is described for the conversion of carboxylic acids into esters, amides, as well as peptides without racemization through carboxyl activation by the reagent combination of POCl3 and DMAP. Long chain alcohols could be converted to the corresponding ester in good yields. 31P NMR spectrum was used to detect phosphorus-containing intermediates in ongoing reactions directly, and a possible mechanism has been proposed based on these results. The Royal Society of Chemistry 2013.
- Chen, Hu,Xu, Xunfu,Liu, Liu,Tang, Guo,Zhao, Yufen
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p. 16247 - 16250
(2013/09/23)
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- Mechanistic studies of DCC/HOBt-mediated reaction of 3-phenylpropionic acid with benzyl alcohol and studies on the reactivities of 'active ester' and the related derivatives with nucleophiles
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Despite of the extensive study for peptide synthesis, DCC-mediated esterification is left still unclear. Therefore, DCC- and DCC/HOBt-mediated reactions of 3-phenylpropionic acid (1) with benzyl alcohol were carried out under several mechanistic considerations. Further, in order to determine the reactivities of the so-called 'active esters' compounds changing the substituents bearing carbonyl and related derivatives group for the purpose of the development of new class of non-symmetry cross-linkers, we have studied the reaction of model compounds, N-(3-phenylpropionyloxy)benzotriazole (6), N-(3-phenylpropionyloxy)phthalimide (7), 3-phenylpropionyloxybenzothiazole (8), and N-(3-phenylpropionyl)benzotriazole (9) with various nucleophiles under similar conditions were carried out for the comparison. It was revealed to exhibit the order of 6>>8>9>7.
- Sheikh, Md. Chanmiya,Takagi, Shunsuke,Yoshimura, Toshiaki,Morita, Hiroyuki
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supporting information; experimental part
p. 7272 - 7278
(2010/10/02)
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- Fluoroalkyldistannoxane Catalysts for Transesterification in Fluorous Biphase Technology
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Novel, practical protocols of transesterification have been advanced with recourse to fluorous biphase technology. The fluoroalkyldistannoxane catalysts enable transesterification in FC-72 solvent to furnish 100% yields of the desired esters by use of reactants ester and alcohol in a 1:1 ratio. The catalysts also work in FC-72/organic solvent system as well as in toluene alone. A number of esters and alcohols bearing various functional groups are employable. The catalysts can be totally recovered and reused. More conveniently, the catalyst solution in FC-72 which is separated from the reaction mixture is directly used for the next reaction.
- Xiang, Jiannan,Orita, Akihiro,Otera, Junzo
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- Steryl and stanyl esters of fatty acids by solvent-free esterification and transesterification in vacuo using lipases from Rhizomucor miehei, Candida antarctica, and Carica papaya
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Sitostanol has been converted in high to near-quantitative extent to the corresponding long-chain acyl esters via esterification with oleic acid or transesterification with methyl oleate or trioleoylglycerol using immobilized lipases from Rhizomucor miehei (Lipozyme IM) and Candida antarctica (lipase B, Novozym 435) as biocatalysts in vacuo (20-40 mbar) at 80 °C, whereas the conversion was markedly lower at 60 and 40 °C. Corresponding conversions observed with papaya (Carica papaya) latex lipase were generally lower. High conversion rates observed in transesterification of sitostanol with methyl oleate at 80 °C using Lipozyme IM were retained even after 10 repeated uses of the biocatalyst. Saturated sterols such as sitostanol and 5α-cholestan-3β-ol were the preferred substrates as compared to Δ5-unsaturated cholesterol in transesterification reactions with methyl oleate using Lipozyme IM. Transesterification of cholesterol with diethyl 1,8-octanedioate using Lipozyme IM in vacuo yielded methylcholesteryl 1,8-octanedioate (75%) and dicholesteryl 1,8-octanedioate (5%). However, transesterification of cholesterol with diethyl carbonate and that of oleyl alcohol with ethylcholesteryl carbonate, both catalyzed by Lipozyme IM, gave ethylcholesteryl carbonate and oleylcholesteryl carbonate, respectively, in low yield (20%). Moreover, cholesterol was transesterified with ethyl dihydrocinnamate using Lipozyme IM to give cholesteryl dihydrocinnamate in moderate yield (56%), whereas the corresponding reaction of lanosterol gave lanosteryl oleate in low yield (14%).
- Weber,Weitkamp,Mukherjee
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p. 5210 - 5216
(2007/10/03)
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- Synthesis, Structure, and Excimer Formation of Aromatic Cholesteric Liquid Crystals
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Cholesteryl ο-arylalkanoates having phenyl, 1-naphthyl, and 1-pyrenyl groups as aromatic groups were synthesized, and some of those were found to form the cholesteric liquid crystal (CLC) phase.The pitch and the screw sense of the helix were determined from the selective reflection wavelength and the circular dichroism.The pitch was around 800 nm for cholesteryl 5-(1-naphthyl)pentanoate and about 970 nm for cholesteryl 3-(1-naphthyl)propionate.The helix sense was left-handed for all cholesteryl esters which form the CLC phase.The orientation of naphthyl groups within each quasi-nematic layer was qualitatively discussed from the sign of cirular dichroism at the 1La absorption band.The short axis of the 1-naphthyl group was parallel to the optical or the molecular axis of the quasi-nematic layer in the CLC of cholesteryl 1-naphthylpropionate and -pentanoate, whereas the short axis of 2-naphthyl group was perpendicular to the optical axis of the CLC of cholesteryl 2-naphthylpropionate.The orientation of the excimer transition moment was investigated by circularly polarized fluorescence spectroscopy.The transition moments for all chromophoric CLC's were found to be nearly perpendicular to the optical axis.From these spectroscopic data, an intralayer excimer configuration for 1- and 2-naphthyl groups was proposed.In the mixture of cholesteryl 3-(1-pyrenyl)propionate (60 molpercent) and 3-phenylpropionate (40 mol percent), the excimer formation was more efficient in the CLC phase than in the crystalline phase.
- Sisido, Masahiko,Takeuchi, Kazuhiko,Imanishi, Yukio
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p. 2893 - 2898
(2007/10/02)
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